1. Field of the Invention
The present invention relates to a method of manufacturing a structure with pores and a structure with pores, and more particularly the structure with pores manufactured by the method of the present invention is usable in a wide range, such as electronic devices, magnetic devices, quantum effect devices as well as optical devices, micro devices, and three-dimensional structures.
2. Related Background Art
 less than Nano Structure greater than 
A thin film, a fine wire, or a dot made of metal or semiconductor having a size smaller than some characteristic length exhibits sometimes significant electrical, optical or chemical performance because a motion of electrons is confined. From this viewpoint, strong attention has been paid to material having a fine structure (nano structure) smaller than several hundreds nanometer (nm), as functional material.
An example of a method of manufacturing a nano structure is semiconductor processing technology such as fine pattern drawing technology including photolithography, electron beam exposure, and x-ray exposure.
In addition to such technology, there is a new approach to realizing a novel nano structure by using as a base a naturally formed regular structure, i.e., self-ordered structure. This approach has been studied in many fields because it is expected that a structure finer and more specific than a conventional method may be manufactured depending upon the kind of a fine structure used as the base.
An example of such a self-ordering approach is anodic oxidation which can manufacture a nano structure having pores of nano size, easily and with good controllability. For example, anodically oxidized alumina is known which is manufactured by anodically oxidizing aluminum and its alloy in acid solution.
 less than Anodically Oxidized Alumina greater than 
A porous oxide coating film can be formed by anodically oxidizing an Al plate in acid electrolytic solution (for example, refer to xe2x80x9cNaturexe2x80x9d, Vol. 337, p.147 (1989) by R. C. Furneaux, W. R. Rigby and A. P. Davidson). The feature of this porous oxide coating film resides in the specific geometric structure that as shown in FIGS. 11A and 11B, ultra fine cylindrical pores (nano holes) 11 having a diameter of several nm to several hundreds nm are disposed in parallel at a pitch (cell size) of several nm to several hundreds nm. These cylindrical pores 11 have a high aspect ratio and are excellent in uniformity of cross sectional diameters.
The nano structure can be controlled to some extent by the conditions of anodic oxidation. For example, it is known that the pore pitch, depth and diameter can be controlled to some extent by an anodic oxidation voltage, time and a pore wide process, respectively.
In order to improve verticality, linearity and independency of pores of an anodically oxidized oxide coating film, a two-step anodic oxidization method has been proposed (refer to xe2x80x9cJapanese Journal of Applied Physicsxe2x80x9d. Vol. 35, Part 2, No. 1B, pp. L126 to L129, Jan. 15, 1996). That is, in this two-step anodic oxidization method, after a porous oxide coating film formed thorough anodic oxidation is once removed, anodic oxidation is again performed to form a porous oxide coating film having pores with improved verticality, linearity and independency. This method utilizes the fact that recesses on the surface of an Al plate, which are formed when the anodically oxidized coating film formed by the first anodic oxidation is removed, become starting points of forming pores by the second anodic oxidation.
In order to improve the controllability of shapes, pitches and patterns of pores of a porous oxide coating film, a method of forming starting points of forming pores by using a stamper has also been proposed (refer to Japanese Patent Application Laid-Open No. 10-121292 by Nakao or xe2x80x9cSolid Physicsxe2x80x9d by Masuda, 31, 493 (1996)). That is, in this method, recesses as pore forming start points are formed by pressing a substrate having a plurality of projections on its surface toward an Al plate, and thereafter anodic oxidation is performed to form a porous oxide coating film having pores with improved controllability of shapes, pitches and patterns. Techniques of forming pores not of a honeycomb shape but of a concentrical shape were reported by Ohkubo et al in Japanese Patent Application Laid-Open No. 11-224422.
Another report by Masuda intends to dispose pores in rows by anodically oxidizing an Al film in a film surface direction, the Al film being sandwiched between insulators (refer to xe2x80x9cAppl. Phys. Lett.xe2x80x9d 63, p. 3155 (1993)).
By paying attention to the specific geometric structure of anodically oxidized alumina, various applications are tried. Although the details of these applications are given by in the explanation by Masuda, some applications will be enumerated below.
For example, there are an application to a coating film by utilizing anti-abrasion and insulation of an anodically oxidized film and an application to a filter made of a peeled-off coating film. Further, by using techniques of filling metal, semiconductor or the like in pores or techniques of forming replicas of pores, various applications are tried to those of coloring, magnetic recording media, EL light emitting elements, electrochronic elements, optical elements, solar batteries, gas sensors and the like. Applications to other fields are also expected, for example, quantum effect devices such as quantum wires and MIM elements, molecule sensors using pores as chemical reaction fields, and the like (refer to xe2x80x9cSolid Physicsxe2x80x9d by Masuda, 31, 493 (1996)).
A nano structure manufacturing method using semiconductor processing technology (e.g., photolithography technology) is, however, associated with the problems of poor manufacture yield and high system cost. A method capable of manufacturing a nano structure with simple processes and with high reproductivity has been desired. Since photolithography basically utilizes a film forming process and an etching process, it is not suitable for a three-dimensional processing method such as forming a circular pore in parallel to the substrate. From this viewpoint, a self-ordering method, particularly, an anodic oxidation method, is preferable because it can manufacture a nano structure relatively easily and with good controllability and can manufacture a large area nano structure. However, there is a limit in the structure controllability so that applications effectively utilizing the significant structure are not realized as yet.
For example, nano holes (pores) in alumina are generally formed in the surface layer of an Al plate and the direction of each pore is perpendicular to the Al plate surface. Further, as described earlier, although the method of forming pores in parallel to the substrate surface was reported, the shapes of pores are likely to become irregular.
An object of the invention is to solve the above problems and provide a structure with pores with good controllability.
Specifically, an object of the present invention is to control the layout, pitch, position, direction, shape and the like of pores to be formed through anodic oxidation and provide a manufacture method of a nano structure, e.g., a nano structure having pores disposed along a specific direction of a substrate.
Another object of the present invention is to provide a manufacture method for a nano structure having a plurality of pore rows with a specific correlation (e.g. pores in upper and lower rows disposed at the same position or at zigzag positions along the column direction).
Further object of the present invention is to provide a method of filling fillers in pores formed by the above-described methods.
Still another object of the present invention is to provide a novel structure with pores formed by the above-described methods
The above objects can be achieved by the invention as in the following.
According to one aspect of the present invention, there is provided a method of manufacturing a structure with pores (holes) which comprises the steps of: disposing a lamination film on a substrate, the lamination film comprising insulating layers and a layer to be anodically oxidized and containing aluminum as a main composition; and performing anodic oxidation starting from an end surface of the lamination film to form a plurality of pores (holes) having an axis substantially parallel to a surface of the substrate, wherein the layer to be anodically oxidized is sandwiched between the insulating layers, and a projected pattern substantially parallel to the axis of the pores (holes) is formed on at least one of the insulating layers at positions between the pores (holes).
The layer to be anodically oxidized is preferably made of aluminum. It is effective in some cases that at least one of the insulating layers is formed by anodic oxidation.
In order to improve regularity, a height of the projected pattern of the insulating layer is preferably {fraction (1/10)} or more of a thickness of the layer to be anodically oxidized
The method may further comprises a step of filling a filler in each of the pores after the step of performing anodic oxidation. The step of filling a filler is preferably performed by plating.
The structure with pores manufactured by the above-described manufacture method provides novel nano structure devices. If an electrode is to be formed to a filler in each pore, it is preferable to form an electrode layer connected to a bottom of each of the pores.
According to another aspect of the present invention, there is provided a method of manufacturing a structure with pores (holes) which comprises the steps of: sandwiching a film containing aluminum as a main composition between first and second insulating films; and anodically oxidizing the film having aluminum as the main composition along a direction substantially perpendicular to a direction of making the first and second insulating films face each other, wherein projections are formed on a surface of at least one of the first and second insulating films in contact with the film containing aluminum as the main composition, the projections controlling a pitch between the pores (holes) to be formed by anodic oxidation.
Next, in order to facilitate to understand the operation of the invention, prior arts will be described with reference to FIGS. 10A and 10B and FIGS. 11A and 11B.
FIGS. 10A and 10B show lateral anodic oxidation pores according to a prior art, and FIGS. 11A and 11B show vertical anodic oxidation pores according to another prior art. In these Figures, reference numeral 11 represents a pore (nano hole), reference numeral 12 represents an anodically oxidized oxide layer containing alumina at its main composition, reference numeral 14 represents a substrate, reference numeral 15 represents a lower insulating layer, reference numeral 16 represents an upper insulating layer, reference numeral 53 represents a barrier layer, and reference numeral 101 represents an Al plate.
Most usual vertical pores of the prior art are shown in FIGS. 11A and 11B. FIG. 11A is a diagram as viewed from the anodically oxidized layer surface side, and FIG. 11B is a cross sectional view taken along line 11Bxe2x80x9411B shown in FIG. 11A. By using the Al plate as an anode, as anodic oxidation is performed in specific acid solution, the surface of the Al plate starts being oxidized. In this case, the Al substrate is oxidized and at the same time specific regions are etched so that pores 11 start being formed in the anodically oxidized layer 12. These pores are formed generally in a direction perpendicular to the Al plate surface. An insulating barrier layer 53 is also formed between the bottom of each pore and the Al plate 101. With this method, there is a distribution of pitches of pores and the position of each pore cannot be controlled. When pores are formed deeply, growth of some pores is stopped in the midst of the forming process or pores are branched with a branching phenomenon. There is therefore a tendency of disordering of pores.
Lateral anodic oxidation pores are shown in FIGS. 10A and 10B. FIG. 10A is a cross sectional view of the anodically oxidized layer cut in parallel to the layer surface near at the central portion thereof, i.e., a cross sectional view taken along 10Axe2x80x9410A shown in FIG. 10B. FIG. 10B is a cross sectional view taken along line 10Bxe2x80x9410B shown in FIG. 10A. As shown, a layer made of an Al thin film to be anodically oxidized is sandwiched between insulating layers and anodic oxidation is performed from one side. Specifically, a lower insulating layer 15, Al layer and upper insulating layer 16 are formed in this order on the substrate 14, and anodic oxidation is performed from one side of this lamination film to form lateral pores. As illustrate in FIG. 10B, similar to the vertical pores, lateral pores are also likely to be disturbed. Intermediate growth stop and branching of pores are therefore likely to occur. As shown, a barrier layer 53 exists between the layer 61 still not anodically oxidized and the pores. The interface of this barrier layer is also disturbed being influenced by the disturbance of pores.
The present inventors have vigorously studied in order to eliminate this disturbance it has been found that by forming projections and recesses on at least one of the upper and lower insulating layers, not only this disturbance is eliminated but also regularity of pores can be controlled not only along the lateral direction but also along the vertical direction if lateral pores are stacked.
This operation may be considered as in the following. There is a tendency that pores having pitches depending upon the conditions of anodic oxidation are formed. This can be ascribed to that the thickness of an insulating film formed between pores depends on the conditions of anodic oxidation. If projections and recesses having a pitch approximately the same as that between pores matching the anodic oxidation conditions are formed on the insulating layer along the pore forming direction, it can be considered that pores are likely to be formed in correspondence with the projections and recesses. Namely, at the position corresponding to the projection of the insulating layer, an insulating layer matching the anodic oxidation conditions is not formed so that pores are likely to be formed at positions of recesses. With this method, a nano structure having pores disposed regularly along a specific direction can be formed.
The term xe2x80x9cregularlyxe2x80x9d used in this specification intends to mean a structure having pore columns having substantially the same pore pitch and diameter, without the disturbed state of pore columns at least in the pore layer such as shown in FIGS. 10A and 10B. The regular structure means a structure having the above-described correlation between positions of pores in respective pore layers and a structure having pores regularly filled with fillers.